Several lines of evidence suggest that dopamine plays a role in the pathophysiology of obsessive-compulsive disorder (OCD). Indeed, some trials have shown the efficacy of neuroleptic addition in the treatment of OCD patients. In this study, we assessed the growth hormone (GH) response to 0.5 mg apomorphine(sc) in 8 drug-free inpatients (6 male, 2 female; mean age +/- SD = 34.7 +/- 12.6) meeting DSM-III-R criteria for OCD without major depression and compared their responses with those of 8 healthy male volunteers (mean age = 27.1 +/- 8.5). The groups did not differ in their mean GH peak response: 12.4 +/- 9.7 ng/mL in OCD patients versus 21.1 +/- 14.2 ng/mL in normal controls (F = 0.9, df1, 14, P = 0.37). These results do not support the hypothesis of dopaminergic overactivity in OCD. In fact, the completely blunted GH response to apomorphine in 2 OCD patients suggests the biological heterogeneity of OCD. Some dopaminergic disturbances could be observed in patients with comorbid diagnoses or patients unresponsive to serotonin reuptake inhibitors, but the results of this study require confirmation from a larger sample with a precise assessment of comorbidity.